The present invention relates to a method and device for controlling the flow of a gaseous medium through a fluid and/or a device. The present invention also relates to the use of a rheologic fluid for various pneumatic applications.
General information concerning rheologic fluids can be found in "An Introduction to Rheology" by H. A. Barnes, J. F. Hutton, and K. Walters, 1989. Also, see U.S. Pat. Nos. 2,417,550 and 2,575,360 for a description of magnetic rheologic effects fluids.
Rheologic fluids, particularly magnetorheologic and electrorheologic fluids, the latter alternatively being known as electroviscous fluids, have interesting properties. These interesting properties include in particular the fact that when a magnetic field is applied to a magnetorheologic fluid and an electrical field is applied to an electrorheologic fluid, a fluid-solid phase transition takes place. Typically a magnetic field on the order of magnitude of approximately 1 kG or an electrical field on the order of magnitude of 1 kV/mm for such a fluid or such a suspension to become solidified is required. This means that the suspension or fluid has a finite flow (plasticity) limit in the field so that each process that occurs is reversible and the degree of fluidity of the suspension or fluid can be intentionally adjusted by changing the strength of the external electrical or magnetic field. The term "fluid" below will be understood to cover liquids and suspensions.
One advantage of an electrorheologic fluid is that the fluids are essentially insulators, so that the power draw is relatively small. Adaptive bumpers and clutches for motor vehicles, for example, can be made with rheologic fluids. Such applications are made possible by the fact that the solidification process takes place on a time scale of approximately 10.sup.-3 to 10.sup.-2 seconds.
Possible electroviscous fluids for example are a mixture of approximately 40 to 60 wt. % silicic acid as the solid, 30 to 50 wt. % of a suitable organic phase with a low electric constant, 5 to 10 wt. % water, and 5 wt. % of a dispersing agent, which have a basic viscosity of 100 to 3000 nPa.s and a mixture with 50 to 60 wt. % of a silicitic acid, 30 to 50 wt. % of an organic phase with a low boiling point, 10 to 50 wt. % water, and 5 wt. % of a dispersing agent such as isododecane.
European Patent 0 222 350 teaches an air spring element in which the spring body is disposed inside a chamber enclosed by a rubber-elastic peripheral wall and two rigid end walls, with the external chamber between the spring body and the peripheral wall, said chamber being divided by the spring body, being filled with an electroviscous liquid controllable by an electrical field.
Unpublished European disclosure 0 590 808 teaches a clutch for a motor vehicle, in which two parts are rotatably connected with each other. These parts move during rotation partially by an electroviscous liquid and a correspondingly greater or lesser coupling of the two parts is controlled by the application of a voltage.
The common feature of these two known applications is that the electrorheologic fluids are used as power transfer media. This has the drawback that the mechanical components, which are frequently made of metal for example, are exposed to the aggressive, particularly chemical, influences of the rheologic fluids. Also, no application can be derived from these two known applications that uses the rheologic fluid, particularly the electroviscous liquid, as a non-power-transferring medium.
Accordingly, the present invention relates to the use of a rheologic fluid as a non-power-transferring medium with in particular any mechanical components not being exposed to the aggressive, in particular chemical, influences of the fluid. Another goal of the present invention is to provide a method and a device for controlling the flow of a gaseous medium through a fluid and uses of a rheologic fluid wherein, in particular, the rheologic fluid is not used as a power-transferring medium and in particular the relatively small yield stress of the rheologic fluid has a non-disadvantageous effect.
These goals are achieved according to preferred embodiments of the invention by providing a system and a method for controlling the flow of a gaseous medium through a fluid which has the following method steps:
provision of a rheologic fluid through which the gaseous medium can be conducted, and PA1 controlling the viscosity of the rheologic fluid. PA1 a rheologic fluid, which is located in particular in the device, PA1 a means of guiding the gaseous medium through the fluid, and PA1 a means for applying a field at least partially in the area of the rheologic fluid.
These features use advantageous properties of rheologic fluids, particularly the property of a rheologic fluid that its degree of viscosity or fluidity can be intentionally changed. This intentional change is based on the microscopic mechanism of the field-induced solidification of the fluid, for which there are various theoretical models in which for example induced dipolar forces or the properties of water bridges play an important role. Here, the previously isotropic material becomes strongly anisotropic when a field or for example external (dynamic) shear forces is/are applied. When an electrical field for example is applied, chains are formed under certain circumstances that are preferably oriented in the direction of the external field.
Preferably, the rheologic fluid is an electrorheologic fluid and/or a magnetorheologic fluid. This makes it particularly easy to change the properties of the fluid. Also preferably the viscosity of the fluid is controlled by applying a controllable field. This simplifies controlling the viscosity of the fluid.
Advantageously, the controllable field is an electrical, magnetic, and/or electromagnetic field. This can be either static or dynamic.
Also preferably the gaseous medium is air, which advantageously makes a number of pneumatic applications possible at low cost.
According to the invention, a rheologic fluid is used for controlling the flow of a gaseous medium by the fluid. Preferably, the rheologic fluid in this case is an electrorheologic and/or a magnetorheologic fluid, which simplifies its use for various applications.
According to the invention, a device for controlling the flow of a gaseous medium through a fluid and/or through a device is characterized by
Preferably, the rheologic fluid is an electrorheologic and/or magnetorheologic fluid. In particular in this case the field can preferably be an electrical, magnetic, and/or electromagnetic field and preferably the means for applying a field can have electrical and/or magnetic and/or electromagnetic components. Such components are for example electrically conducting wires, electrically conducting plates, capacitors, or electromagnets, and, since the power draw of the rheologic fluid is relatively low, for example conducting plastics as well.
Preferably, the gaseous medium is air. This choice leads to for example electropneumatic devices at low cost. If preferably the means of guiding the gaseous medium are strips, which are located in the device and at least partially wetted by the fluid, the path of the gaseous medium is more precisely specified and in particular can be extended, which can in particular lead to a stronger blockade or slower flow of the gaseous medium through the fluid.
If preferably the fluid is at a distance from chemically vulnerable materials, the service life or operating time of such devices is prolonged.
According to certain preferred embodiments of the invention the device just described is used as a component for an overpressure valve. In this case, the pressure point is preferably set by the strength of the field applied. The higher the field applied, the higher the pressure point. In particular, in this application of the device, it must be borne in mind that the direction in which the field is applied makes a difference for certain anisotropic rheologic fluids.
According to the invention at least one of the devices described is used as a component of a control valve. In one application of one of the above-mentioned devices as a component for a control valve, it is possible to connect corresponding consumers such as pumps or cylinders for example.
Advantageously, an overpressure valve is created by one of the above-described devices, in which a pressure point can be set by the strength of the field applied.
Also, a control valve is advantageously characterized by at least two of the above-described devices, providing an outlet and an inlet for the gaseous medium and connecting the outlet of one of the devices with the inlet of the other device. Preferably, a consumer can be linked to the connection between the two devices. This measure makes an advantageous electropneumatic device available.
Advantageously, one of the above-mentioned devices is used for pneumatic control and/or regulation.
In the context of this invention, "control" also means "regulation," meaning that whenever the term "control" is used in the context of this invention, it also covers the meaning of "regulation."
The invention will now be described without limitation of the general inventive idea on the basis of embodiments with reference to the drawings, to which express reference is made as well regarding the disclosure of all of the details according to the invention that are not explained in greater detail in the text.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.